1. Field of the Invention
The present invention relates to power supply control apparatuses and particularly to power supply control apparatus having a function supplying power supply voltage to equipment cabled thereto.
2. Description of the Background Art
Generally in audio and video systems a video signal output device (e.g., an optical disc reproduction device) outputting a video signal and a display or a similar video image display device (e.g., a television (TV) receiver) are connected with a cable. If the cable transmits a signal having an inappropriate magnitude in voltage or passes a current having an inappropriate magnitude, the device may fail. Accordingly in such systems such problem must be prevented.
For example Japanese Patent Laying-open No. 2004-234540 describes that a power supply voltage that is supplied to equipment is divided by a resistor and then input to an analog/digital (A/D) port and measured and in accordance with the measurement result a current to be supplied to a load is controlled with an electronic switch (a field effect transistor: FET).
Furthermore, Japanese Patent Laying-open No. 05-215792 indicates a battery voltage detection circuit. When the battery voltage detection circuit detects that a battery's voltage divided by a resistor has a value indicating a level below a preset threshold voltage of an analog port, a light emitting diode is turned on to issue an alarm.
In recent years a High Definition Multimedia Interface (HDMI) specification has been proposed as a specification of an interface for interconnecting video equipment, and products having an interface function in conformity with the HDMI specification are being introduced into the market. The HDMI specification is a digital video interface (DVI) serving as a standard specification for connecting a personal computer and a display together, plus a function based on the DVI for accommodating household electrical appliance.
The HDMI specification, item 4.2.7 defines that any source equipment (equipment outputting a video signal, e.g., an optical disc reproduction device) be capable of supplying a current of at least 55 mA from a power supply pin serving to supply a direct current (DC) power supply voltage of +5 V and that a supply voltage in doing so be maintained in a range of 4.8 V to 5.3 V. Furthermore, the same item defines that if a current of at least 0.5 A flows, overcurrent protection be required.
However, neither Japanese Patent Laying-open No. 2004-234540 nor 05-215792 specifically discloses a method for preventing an overcurrent flowing through a cable for information equipment including video equipment.